1. Field of the Invention
The present invention relates to a method for redrawing of glass, an apparatus for conducting of said method and a glass component which can be prepared by said method.
2. Description of Related Art
In principle, the redrawing of glasses is known, in particular a comprehensive state of the art about the redrawing of blanks and/or blanks with circular cross-section for the drawing of glass fibers exists.
During a redrawing method a glass piece is partially heated and drawn in the longitudinal direction with the help of suitable mechanical equipment. When the glass piece—the blank—is fed into a heating zone at a constant speed and when the heated glass is drawn with a constant speed, then this results in a reduction of the cross-section shape of the blank which depends on the ratio of the speeds. So, when e.g. tubular blanks are used, then again tubular products are prepared, but with smaller diameter. The cross-section shape of the products is similar to that of the blank, wherein for the most part it is even desirable to achieve a reproduction of the blank in a reduced scale of 1:1 by suitable measures (see EP 0 819 655 B1).
In a step of redrawing glasses normally an oblong blank is fixed on one end in a holder and heated at the other end in for example a muffle kiln. Once the glass has become deformable, it is drawn by the exertion of drawing force at the end of the blank being fixed in the holder. When during that the blank is moved forward into the muffle, then with a suitable selection of the temperatures this results in a product with a smaller cross-section, but a similar geometry. For example, a blank with circular cross-section is drawn into a glass fiber. The selection of the speeds of drawing the product, for example a component, and optionally moving forward the blank determines the reduction factor of the cross-section. Normally, the ratio of thickness to width of the cross-section of the blank remains constant. In the case of drawing glass fibers this is desired, because starting from a blank with circular cross-section a glass fiber having also a circular cross-section can be drawn.
It has been proved that it is difficult to redraw flat components, i.e. components having a ratio of width to thickness of the cross-section of for example 80:1. Only with blanks having a very high width it is possible to draw components having also a high width. So e.g. from a blank having a cross-section of 70 mm (millimeter) width and 10 mm thickness (B/D=7) a component having a cross-section of 7 mm width and 1 mm thickness (b/d=7) can be produced.
A component having a cross-section with a higher width and the same thickness is only possible, when a blank having a cross-section with a higher width or a lower thickness is used. The use of a blank having a higher width often fails due to the impossible producibility, and the use of a blank having a lower thickness is increasingly inefficient, since the blank during redrawing has to be exchanged more often.
In U.S. Pat. No. 7,231,786 B2 is described, how plane glass panes can be produced by redrawing. For achieving a product with higher width, in this case grippers are used which draw the soft glass into the width direction, prior to expanding the glass into the longitudinal direction with the help of edge rollers.
In U.S. Pat. No. 3,635,687 A a redrawing method is described, in which by cooling of the edge region of the flat blank a change of the ratio of width to thickness (B/D) is achieved. But with this method a maximum increase of the ratio of width to thickness by a factor of 10.7 can be achieved. The edge cooler used there is arranged such that only a small part of the edge regions in the deformation zone of the blank is cooled. So the temperature difference between the center region of the blank and the edge regions decreases very quickly again.
In EP 0 819 655 B1 a method for forming glass is described. In this case in a forming step also redrawing can be used. But it is not described, how the ratio of width to thickness (B/D) is adjusted. Here after heating the glass is locally heated or cooled for manipulating the geometry.
Each of these manipulations described in these references only results in a smaller change of the geometry of the blank in comparison to the final shape and/or to the shape of the drawn component. Furthermore, these methods are associated with relatively high effort. In particular in the case, when grippers or rolls should be used, a sophisticated redrawing apparatus is required which is susceptible to defects.
Thus, the object of the present invention is the provision of an efficient method for the production of glass components. Furthermore, a method should be provided which makes it possible to increase the ratio of width to thickness of the blank (B/D) in comparison to the ratio of width to thickness of the glass component produced (b/d). In particular, a method for the production of flat glass components should be provided, through which from a blank having a width B and a thickness D a flat glass component having a width b and a thickness d can be prepared, wherein the ratio b/d is much higher than the ratio B/D.